Chinese police shot dead 13 people in Xinjiang after they drove into a police building and set off an explosion Saturday, regional authorities said, in the latest attack to hit the restive region.

The vast area in China's far west, home to the mainly Muslim Uighur ethnic minority, has faced a series of violent attacks in recent years.

Beijing has vowed a year-long crackdown on terrorism in recent weeks following several high-profile attacks blamed on Xinjiang militants, which since late last year struck outside the region and targeted ordinary citizens rather than government or security personnel.

"Today thugs crashed a car into the public security building of Kargilik county in Xinjiang's Kashgar prefecture and set off an explosion. Police took decisive action and shot dead 13 thugs," the official Xinjiang government website Tianshan reported.

Three police suffered injuries but there were no other casualties, the report said, without providing further details. It was unclear if the attackers used one or more explosive devices.

The state news agency Xinhua described the vehicle as a truck and said the attack happened in the morning, adding that authorities were investigating and "local social order is normal".

China's most powerful body, the Politburo Standing Committee, said in May that "cracking down on violent terrorist activities must be the focal point of the current struggle", Xinhua reported at the time.

Authorities have announced hundreds of detentions or criminal punishments, including the sentencing of 55 people in late May for offences such as terrorism at a ceremony in a stadium attended by 7,000 people.

This week China executed 13 people for "terrorist attacks" in Xinjiang and ordered the death penalty for three others for a car crash last October in Beijing's Tiananmen Square, the symbolic heart of the Chinese state.

In that incident, the first major event blamed on Xinjiang residents to take place outside the region, three family members drove onto the popular tourist area, killing two people and wounding 40 before the car burst into flames and they themselves died.

- Targeting ordinary citizens -

In another major incident in March, dubbed China's "9/11" by state media, attackers went on a stabbing spree at a railway station in the southwestern city of Kunming that left 29 people dead and 143 wounded.

On April 30, the final day of a visit by Chinese President Xi Jinping to Xinjiang, attackers armed with knives and explosives killed one person and wounded 79 at a railway station in the capital Urumqi.

The next month assailants in Urumqi threw explosives and ploughed into a crowd at a market, leaving 39 people killed, along with four attackers, and more than 90 wounded.

Overseas rights groups blame the unrest in part on cultural repression and harsh security measures against Uighurs while Xinjiang's economic growth mostly benefits an influx of China's ethnic majority Han.

Riots erupted between the two ethnic groups in Urumqi in 2009, leaving about 200 people dead.

Dilshat Rexit, spokesman for the exiled World Uyghur Congress urged China to "stop its suppression and change its provocative policies".

"Shooting dead protesters and accusing them of terrorism is to avoid the root of the problem," he said in an emailed statement.

Beijing counters that it has brought rapid development to the area and blames the violence on separatist militant groups backed by overseas organisations.

But security experts have cast doubt on the strength of any resistance movement inside Xinjiang or its links to foreign groups.

Information from the area is difficult to verify, with journalists subject to heavy restrictions.

Rights groups have expressed concerns about whether terror suspects can receive fair trials, given the common use of forced confessions in China's legal system.

China's courts are effectively controlled by the ruling Communist Party and have a near-total conviction rate.